That is the first truly great reason I have heard for insisting that a solution not use modules. One more absolute that now has to be moderated with an except... =)

In the future, you should mention that up front when you insist on core features only, that way if someone is really ornery, they might just find a vile way to load the module they want as a bonus...

--
$you = new YOU;
honk() if $you->love(perl)